Surviving breast cancer

Women diagnosed with breast cancer also have a greater burden of other illness

Although breast cancer is worldwide the most common cancer in women, many, perhaps most patients die from other causes. In Australia, it is estimated that 17 730 people will have been diagnosed with breast cancer in 2017, and that there will have been 3114 breast cancer-related deaths: this represents 13% of all new cancer diagnoses, but only 6.5% of cancer deaths.1 The difference between incidence and mortality has been widening for several decades, with a continual increase in incidence but a substantial fall in mortality. Five-year survival has increased from 70% in the 1980s to 90%,1 primarily because of earlier diagnosis and improved treatment.

Increased survival has led to a large and growing population of people who have been diagnosed with breast cancer, many of whom are probably cured. In the United States, for example, there are about 3 million breast cancer survivors, equivalent to almost 1% of the population;2 in Australia, in 2012 it was estimated that 193 730 women were alive who had been diagnosed with breast cancer at some point in the previous 31 years,1 equivalent to 0.8% of the population.

This patient population is receiving increasing attention, and their unique and broad range of problems and needs are being acknowledged. These include physical and medical problems, as well as concerns about fertility, sexual health, and psychosocial, spiritual, and existential questions. The concept of “survivorship” has developed to encompass this broad area, defined by the US National Coalition for Cancer Survivorship as “living with, through and beyond cancer”, and covers the time from diagnosis of cancer through the balance of life.3 This concept has opened the door to many opportunities for improving the long term outcomes of people who have been treated for cancer. Many health services are developing survivorship care planning models for survivors of breast and other cancer types.4

One area deserving greater emphasis in the care of breast cancer survivors is comorbidity development, as for many it is these conditions, rather than breast cancer, that will lead to death. For example, in the long term follow-up of a large study of extended adjuvant endocrine treatment of post-menopausal women, 60% of patients died of a non-breast cancer cause, and for patients over 70 years of age a non-breast cancer death was seen in 72%.5 Second cancers and cardiovascular disease were the most common causes of non-breast cancer-related deaths. For long term optimal care of breast cancer patients, appropriate preventive and surveillance strategies for other serious health issues are thus vital.

In this issue of the MJA,6 Ng and colleagues report their investigation of whether patients treated for breast cancer are at greater risk of developing comorbidities than women of the same age without cancer. Although the published results from previous studies of this question are not entirely consistent, the balance of evidence suggests that the risk is, in fact, higher for women treated for breast cancer. Two cross-sectional studies from US population surveys of cancer survivors7,8 and one case–control study9 found more frequent development of comorbidity following a breast cancer diagnosis, with the latter study suggesting that women receiving multimodality treatment were most affected; notably, the rates of comorbidity among cases and controls was similar at baseline as in the study by Ng and her co-authors.9 A fourth study,10 on the other hand, found that comorbidity development was similar for women with or without breast cancer.

Ng and colleagues analysed Pharmaceutical Benefits Scheme data on the prescribing of specific medication types. They necessarily made a number of assumptions about these data, and their population of women with breast cancer was limited to hormone receptor positive cases and holding a concession card. The authors also discuss several factors related to receiving a breast cancer diagnosis that might explain their findings, including factors that might increase the likelihood of detecting a comorbidity, such as increased health awareness and care. There are also other factors that might exaggerate the diagnosis of comorbidities, such as the use of medications for managing the side effects of cancer treatment rather than comorbidities, for example, antidepressant agents for reducing hot flushes, proton pump inhibitors for dyspepsia associated with chemotherapy or corticosteroids or angiotensin-converting enzyme (ACE) inhibitors for managing short term falls in left ventricular function. Whether the small but statistically significantly elevated frequencies (hazard ratios, 1.2–1.4) for most of the comorbidities examined, including diabetes, cardiovascular disease, depression, gastric acid disorders, osteoporosis, and pain and inflammation, can be explained by these methodological issues remains possible.

However, given the consistency with previously published research, the study by Ng and her co-authors lends further support to the idea that treatments for breast cancer can accelerate ageing and facilitate the development of comorbidities. Alfano and colleagues9 postulate that breast cancer and its treatment lead to elevated inflammatory cytokine levels, increasing the risk of comorbidities; the association between various risk factors for breast cancer and other health problems may also play a role. Further research to confirm these findings and to investigate the mechanisms of increased comorbidity development and mitigation strategies is warranted.